Liquid crystal display device having touch sensor embedded therein, method of driving the same and method of fabricating the same

ABSTRACT

A liquid crystal display device having a touch sensor embedded therein is disclosed. The present invention includes a liquid crystal layer between first and second substrates, a pixel on the second substrate to apply a horizontal electric field to the liquid crystal layer, a touch sensor on the second substrate, the touch sensor detecting a touch by forming a touch capacitor with a touch object for touching the first substrate, and a readout line outputting a sensing signal from the touch sensor. The touch sensor includes a sensing electrode on the second substrate to form the sensing capacitor with the touch object, first and second sensor gate lines, a first sensor thin film transistor supplying a sensing driving voltage to the sensing electrode in response to a control of the first sensor gate line, and a second sensor thin film transistor supplying electric charges of the sensing electrode as the sensing signal in response to a control of the second sensor gate line.

The present patent document is a divisional of U.S. patent applicationSer. No. 12/980,855 filed on Dec. 29, 2010, which claims priority to theKorean Patent Application No. 10-2010-0060844, filed in Korea on Jun.25, 2010, which are hereby incorporated by reference as if fully setforth herein.

BACKGROUND

1. Field of the Invention

The present disclosure relates to a liquid crystal display device havinga touch sensor embedded therein, method of driving the same and methodof fabricating the same. Although the present disclosure is suitable fora wide scope of applications, it is particularly suitable for a slim andlight liquid crystal display having a touch sensor embedded therein.

2. Discussion of the Related Art

Recently, touchscreens that enable information input to a screen of adisplay are widely applied as information input devices for a computersystem. Since a user is able to move or select display information bysimply touching a screen with a finger or stylus pen, a touchscreen iseasy to use for men and women of all ages.

A touchscreen outputs touch information by detecting a touch performedon a display screen and a corresponding touched position. A computersystem analyzes the touch information and then executes a correspondingcommand.

Flat panel display such as a liquid crystal display (LCD), a plasmadisplay panel (PDP), an organic light emitting diode (OLED) display andthe like are widely used as displays.

Touchscreen technology includes one of a resistant film type, acapacitance type, an infrared type, an ultrasonic type, anelectromagnetic type and the like according to a sensing principle.Specifically, the resistant film type touchscreen or the capacitancetype touchscreen is widely used due to their advantages of manufacturingcost.

A resistant-film type touchscreen is configured to detect a touch bysensing a change of voltage generated when top and bottom resistantfilms (transparent conductive films) come in contact with each other bya touch pressure. Yet, a touchscreen or display is vulnerable to a touchpressure applied to the resistant-film type touchscreen. And, theresistant-film type touchscreen has a low transmissivity due to lightscattering in an air layer between resistant layers.

A touchscreen of a capacitance type, which compensates the disadvantagesof the resistant-film type, detects a touch by sensing a change ofcapacitance generated when a small quantity of electric charges move toa touch point touched with a human body or stylus pen. The capacitancetype touchscreen uses a tempered glass, thereby receiving wide attentiondue to its strong durability, high transmissivity, excellenttouch-sensing capability and multi-touch feasibility.

Generally, a touchscreen is manufactured as a panel and is then attachedto a topside of a display to perform a touch input function.

However, a touch panel attached display is manufactured in a manner ofattaching a separately fabricated touch panel to a display, whereby amanufacturing cost is raised. Moreover, as overall volume and weight ofa system increase, mobility of the corresponding system is lowered orlimitation is put on designing the corresponding system.

BRIEF SUMMARY

A touch sensor embedded liquid crystal display device includes a liquidcrystal layer between top and bottom substrates, a pixel provided toeach pixel area of the bottom substrate to apply a horizontal electricfield to the liquid crystal layer in the pixel area using a pixelelectrode supplied with a data signal via a thin film transistorconnected to gate and data lines and a common electrode connected to acommon line, a touch sensor provided to each space between one group ofpixels and another group of pixels on the bottom substrate, the touchsensor detecting a touch by forming a touch capacitor with a touchobject for touching the top substrate, and a readout line outputting asensing signal from the touch sensor. In this case, the touch sensorincludes a sensing electrode provided to the bottom substrate to formthe sensing capacitor with the touch object, first and second sensorgate lines, a first sensor thin film transistor supplying a sensingdriving voltage to the sensing electrode in response to a control of thefirst sensor gate line, and a second sensor thin film transistorsupplying electric charges of the sensing electrode as the sensingsignal in response to a control of the second sensor gate line.

Preferably, the first and second sensor gate lines are sequentiallydriven.

In another aspect of the present invention, a method of driving a liquidcrystal display device, in which a touch sensor is embedded, includesthe steps of storing data in a plurality of pixels by driving gate anddata lines in a data write interval, applying a horizontal electricfield according to data to a liquid crystal layer of each pixel, anddetecting a touch according to an electrostatic capacitance formedbetween a touch object touching a top substrate of the liquid crystaldisplay device and the touch sensor by driving the touch sensor providedto each space between one group of pixels and another group of pixels,the touch detecting step including the steps of supplying a powervoltage to a sensing electrode of the touch sensor by driving a firstsensor thin film transistor and outputting electric charges of thesensing electrode generated from the touch detection to a readout lineas a sensing signal.

In a further aspect of the present invention, a method of fabricating atouch sensor embedded liquid crystal display device includes the stepsof forming a gate metal pattern including gate electrodes of a pixelthin film transistor and first and second sensor thin film transistorson a substrate together with a gate line, a common line and first andsecond sensor gate lines, forming a common electrode connected to thecommon line, forming a gate insulating layer on the substrate having thegate metal pattern and the common electrode formed thereon, formingsemiconductor layers of the pixel and first and second sensor thin filmtransistors on the gate insulating layer, respectively, forming a datametal pattern including source and drain electrodes of the pixel andfirst and second sensor thin film transistors on the gate insulatinglayer having the semiconductor layers formed thereon together with adata line, a power line and a readout line, forming a passivation layerto cover the data metal pattern, forming a plurality of contact holes inthe passivation layer, forming a pixel electrode on the passivationlayer to be connected to the drain electrode of the pixel thin filmtransistor via the contact hole to form a horizontal electric field withthe common electrode; and forming a sensing electrode together with thegate line, the common electrode, or the pixel electrode.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a schematic diagram of a vertical polyhedral structure of aliquid crystal display device having a touch sensor embedded thereinaccording to an embodiment of the present invention;

FIG. 2 is a schematic block diagram of a liquid crystal display devicehaving a touch sensor embedded therein according to an embodiment of thepresent invention;

FIG. 3 is a diagram for configuration of a single frame in a liquidcrystal display device h according to an embodiment of the presentinvention;

FIG. 4 is a diagram of an equivalent circuit for partial pixels of aliquid crystal display device having a touch sensor embedded thereinaccording to an embodiment of the present invention;

FIG. 5 is a diagram of driven waveforms for the equivalent circuit shownin FIG. 4;

FIG. 6 is a layout of a TFT substrate for the equivalent circuit of theliquid crystal display device shown in FIG. 4; and

FIG. 7 is a cross-sectional diagram of the TFT substrate bisected alongthe cutting lines I-I′ and II-II′ shown in FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a schematic diagram of a vertical polyhedral structure of aliquid crystal display device having a touch sensor embedded thereinaccording to an embodiment of the present invention.

Referring to FIG. 1, a liquid crystal display (hereinafter abbreviatedLCD) device includes a top substrate 50, a bottom substrate 60 and aliquid crystal layer 70 provided between the top and bottom substrates50 and 60.

On the bottom substrate 60, a thin film transistor (hereinafterabbreviated TFT) substrate including a plurality of pixels PX and aplurality of touch sensors TS are formed. In this case, each of thetouch sensors TS is provided to each space between adjacent pixelgroups, each of which includes a plurality of the pixels. So to speak, aplurality of the pixels PX are located between the adjacent touchsensors TS to each other. Each of the pixels PX drives the liquidcrystal layer 70 in in-plane switching (IPS) mode or fringe fieldswitching mode by applying a horizontal electric field to the liquidcrystal layer 70. For this, each pixel PX includes a pixel electrodesupplied with a data signal via a TFT connected to gate and data linesand a common electrode supplied with a common voltage to apply thehorizontal electric field to the liquid crystal layer 70 together withthe pixel electrode. Since each pixel PX of the bottom substrate 60applied the horizontal electric field applied to the liquid crystallayer 70, an electrode for driving the liquid crystal layer is notnecessary for the top substrate 50. On the top substrate 50, formed area black matrix defining the pixels PX and a color filter array includingred, green and blue color filters respectively corresponding to thepixels PX. And, the LCD device further includes top and bottompolarizing plates attached to outer surfaces of the top and bottomsubstrates 50 and 60 to have optical axes orthogonal to each other,respectively and top and bottom alignment layers respectively providedto inner surfaces contacting with liquid crystals to set a pre-tiltangle of the liquid crystals.

If a user touches a surface of the top substrate 50 with such aconductive touch object as a human body, a stylus pen and the like, thetouch object and the touch sensor TS on the bottom substrate 60 formcapacitance, i.e., a sensing capacitor Cf in a manner of leaving the topsubstrate 50 and the liquid crystal layer 70 in-between. The touchsensor TS detects a capacitance change according to the formation of thesensing capacitor Cf and then outputs a sensor signal indicating thecorresponding touch.

FIG. 2 is a schematic block diagram of a liquid crystal display devicehaving a touch sensor embedded therein according to an embodiment of thepresent invention.

Referring to FIG. 2, an LCD device includes an LCD panel 10 having aplurality touch sensors TS embedded therein together with a plurality ofpixels PX, a gate driver 12 driving a plurality of gate lines GL of theLCD panel 10, a data driver 14 driving a plurality of data lines DL ofthe LCD panel 10, a sensor gate driver 16 driving a sensor gate line SGLof the LCD panel 10, and a readout circuit 18 detecting a touch bymonitoring an output of a readout line ROL of the LCD panel 10.Optionally, in FIG. 2, the readout circuit 18 is built in the datadriver 14 and/or the sensor gate driver 16 is built in the gate driver12. The sensor gate driver 16 may be positioned at an opposite side tothe gate driver 12

The LCD panel 10 includes a plurality of pixels PX defined in a mannerthat a plurality of the gate lines GL and a plurality of the data linesDL cross with each other. And, each touch sensor TS is provided to aspace between one group of the pixels PX and another group of the pixelsPX. The touch sensor TS driven by a pair of the sensor gate lines SGLaand SGLb, detects a touch using a capacitance, and then outputs asensing signal to the readout line ROL. A first sensor gate line SGLa ofthe sensor gate line pair SGLa and SGLb is first driven to determine aduration for supplying a sensing driving voltage Vd to the correspondingtouch sensor TS. Subsequently, a second sensor gate line SGLb is drivento determine a duration for outputting the sensing signal to the readoutline ROL from the corresponding touch sensor TS.

The readout line ROL is provided to each space between one group of thedata lines DL and another group of the data lines DL in parallel withthe corresponding data line DL and is connected to a plurality of thetouch sensors TS arranged in a vertical direction. The sensor gate linepair SGLa and SGLb is provided to each space between one group of thegate lines GL and another group of the gate lines GL in parallel withthe corresponding gate line GL and is connected to a plurality of thetouch sensors TS arranged in a horizontal direction. A plurality of thesensor gate lines SGL are independently driven per line. Alternatively,if a plurality of the sensor gate lines SGL are grouped by apredetermined number unit, a predetermined number of the first sensorgate lines SGLa are driven in common and a predetermined number of thesecond sensor gate lines SGLb are driven in common. As a plurality ofthe touch sensors TS are arranged in a matrix form, multiple touches canbe simultaneously detected.

The LCD panel 10, as shown in FIG. 3, is driven in a manner that a frameinterval 1F is divided into a data write interval DWM for storing datain a pixel PX and a touch sensing interval TSM for driving a touchsensor TS. For instance, referring to FIG. 3(A), a frame 1F can bedivided into a data write interval DWM for storing data signals in aplurality of pixels PX by scanning a plurality of gate lines GL for thefirst half and a touch sensing interval TSM for driving a touch sensorTS by scanning a plurality of sensor gate lines SGLa and SGLb for thesecond half. Meanwhile, referring to FIG. 3(B), a frame 1F is dividedinto a plurality of horizontal intervals (e.g., horizontal lines),whereby a data write interval DWM and a touch sensing interval TSM canalternate with each other.

In the data write interval DWM, the gate driver 12 sequentially drives aplurality of the gate lines GL. And, the data driver 14 supplies a datasignal to a plurality of the data lines DL each time the gate line GL isdriven.

In the touch sensing interval TSM, the sensor gate driver sequentiallydrives the first and second sensor gate lines SGLa and SGLb. And, thereadout circuit 18 detects a touch and a touched position by receivingan input of a sensing signal from the touch sensor TS having detectedthe touch via the readout line ROL. In doing so, the readout circuit 18detects the touch by integrating an output current of the readout lineROL per unit time. The readout circuit 18 detects a touched position(e.g., XY coordinates) based on position information (e.g., Xcoordinate) of the readout line ROL and position information (e.g., Ycoordinate) of the driven sensor gate line pair SGLa and SGLb. And, thereadout circuit 18 is able to detect multiple touches simultaneouslyoccurring at different points via the touch sensor TS and the readoutline ROL.

FIG. 4 is a diagram of an equivalent circuit for partial pixels of aliquid crystal display device having a touch sensor embedded thereinaccording to an embodiment of the present invention, and FIG. 5 is adiagram of driven waveforms for the equivalent circuit shown in FIG. 4.

Referring to FIG. 4, an LCD device includes a plurality of pixels PX anda touch sensor TS of a capacitance type provided to each space betweenone group of pixels PX and another group of pixels PX.

Each of the pixels PX includes a pixel TFT Tpx provided to each pixelarea defined by gate and data lines GLi and DL crossing with each other,a liquid crystal capacitor Clc connected between the pixel TFT Tpx and acommon line CLi, and a storage capacitor Cst connected between the pixelTFT Tpx and the common line CLi in parallel with the liquid crystalcapacitor Clc. In particular, the gate line GLi and the common line CLiare formed in parallel with each other by leaving the pixel areain-between. The liquid crystal capacitor Clc includes a pixel electrodeconnected to the pixel TFT Tpx, a common electrode connected to thecommon line CLi and a liquid crystal layer having a horizontal electricfield applied thereto by the pixel and common electrodes. And, thestorage capacitor Cs is formed in a manner that the pixel and commonelectrodes are overlapped with each other by leaving an insulating layerin-between.

The pixel TFT Tpx, as shown in FIG. 5, supplies a data signal DS fromthe data line DL to be stored in the liquid crystal capacitor Clc andthe storage capacitor Cst in response to a gate-on voltage Von of a gatesignal from the corresponding gate line GLi in a data write intervalDWM. Liquid crystals are driven by the data signal stored in the liquidcrystal capacitor Clc. And, the storage capacitor Cst enables the liquidcrystal capacitor Clc to maintain the data signal stably.

A touch sensor TS is provided to a space between the gate line GLi and astorage line (not shown in the drawing) of a next stage. The touchsensor TS includes a sensing electrode 20 for forming a sensingcapacitor Cf together with a touch object, a sensor gate line pair SGLaand SGLb, a first sensor TFT Tsw1 forming one current path between apower line PL (or a common line CLi) and one end portion of the sensingelectrode 20 in response to a control of the first sensor gate lineSLGa, and a second sensor TFT Tsw2 forming another current path betweena readout line ROL and the other end portion of the sensing electrode 20in response to a control of the second sensor gate line SGLb. Inparticular, the touch sensor TS is provided to a space between one groupof n pixels (n: natural number) and another group of n pixels inconsideration of a size of a touch point. For instance, if a line widthof a touch point is about 4 mm, the touch sensor TS can be provided tothe space between 50 pixels and 50 pixels.

The sensor gate line pair SGLa and SGLb is formed in parallel with thegate line GLi. And, the sensing electrode 20 is formed between thesensor gate lines SGLa and SGLb in a manner of being separated by atouch sensor unit. The power line PL and the readout line ROL are formedin parallel with the data line DL by leaving a plurality of the datalines DL in-between.

In the first sensor TFT Tsw1, a gate electrode is connected to the firstsensor gate line SGLa, a source electrode is connected to the power linePL or the common line CLi, and a drain electrode is connected to one endportion of the sensing electrode 20. The source electrode and the drainelectrode can be switched to each other according to a currentdirection. The first sensor TFT Tsw1 supplies a sensing driving voltageVd from the power line PL to the sensing electrode 20 in response to agate signal supplied to the first sensor gate line SGLa. The firstsensor TFT may be connected to the common line CLi instead of the powerline PL and supplies the common voltage as the sensing driving voltageVd to the sensing electrode 20. In this case, the power line PL may beomitted.

In the second sensor TFT Tsw2, a gate electrode is connected to thesecond sensor gate line SGLb, a source electrode is connected to thereadout line ROL, and a drain electrode is connected to the other endportion of the sensing electrode 20. The source electrode and the drainelectrode can be switched to each other according to a currentdirection. Once a touch capacitor Cf is formed, the second sensor TFTTsw2 outputs a sensing signal proportional to a size of the touchcapacitor Cf to the readout line ROL.

Particularly, the first sensor TFT Tsw1 is turned on by the gate-onvoltage Von of the first sensor gate line SGLa in the touch sensinginterval TSM shown in FIG. 5 and then supplies the sensing drivingvoltage Vd from the power line PL to the sensing electrode 20. While thegate-on voltage Vd is supplied to the sensing electrode 20, if a surfaceof the LCD device is touched with a touch object, the sensing capacitorCf is formed between the touch object and the sensing electrode 20. Indoing so, referring to Formula 1, an electric charge quantity Q1supplied to the sensing electrode depends on a multiplication of thesensing driving voltage Vd supplied to the sensing electrode 20 and asum of an electrostatic capacitance of the sensing capacitor Cf and aparasitic electrostatic capacitance Cpara formed between the sensingelectrode 20 and a neighbor line.

Q1=(Cf+Cpara)×Vd   [Formula 1]

Subsequently, the second sensor TFT Tsw2 is turned on the gate-onvoltage Von of the second sensor gate line SGLa in the touch sensinginterval TSM shown in FIG. 5 and then outputs a sensing signal, whichcorresponds to the electric charge quantity Q1 derived to the sensingelectrode 20 by the touch to the sensing electrode 20, to the readoutline ROL. In doing so, if a reference voltage Vref is supplied to thereadout line ROL from the readout circuit, referring to Formula 2, anelectric charge quantity delivered to the readout line ROL from thesensing electrode 20 via the second sensor TFT Tsw2 is determined as amultiplication (Cf+Cpara)×(Vd−Vref) of “a sum (Cf+Cpara) of anelectrostatic capacitance of the sensing capacitor Cf and a parasiticelectrostatic capacitance Cpara formed between the sensing electrode 20and a neighbor line” and “a voltage difference (Vd−Vref) between thepower voltage Vd supplied to the sensing electrode 20 and the referencevoltage Vref supplied to the readout line ROL”.

Q2=(Cf+Cpara)×(Vd−Vref)   [Formula 2]

Hence, a sensing signal (i.e., an output current) proportional to theelectric charge quantity Q2 outputted from the second sensor TFT Tsw2 tothe readout line ROL is determined in proportion to a size of anelectrostatic capacitance of the sensing capacitor. The readout circuitdetects a touch by integrating the output current of the readout lineROL.

Therefore, since the sensing signal outputted to the readout line ROLfrom the sensing electrode 20 having detected the touch via the secondsensor TFT Tsw2 is only determined by “a sum (Cf+Cpara) of anelectrostatic capacitance of the sensing capacitor Cf and a parasiticelectrostatic capacitance Cpara formed between the sensing electrode 20and a neighbor line” and “a voltage difference (Vd−Vref) between thepower voltage Vd supplied to the sensing electrode 20 and the referencevoltage Vref supplied to the readout line ROL”, it is able to output aprecise sensing signal irrespective of a threshold voltage Vth despitethat the threshold voltage Vth of the second sensor TFT Tsw2 isdifferent.

FIG. 6 is a layout of a TFT substrate for the equivalent circuit of theliquid crystal display device shown in FIG. 4, and FIG. 7 is across-sectional diagram of the TFT substrate bisected along the cuttinglines I-I′ and II-II′ shown in FIG. 6.

Referring to FIG. 6 and FIG. 7, in a TFT substrate, a common line CLi, agate line GLi, a sensing electrode 20 and sensor gate lines SGLa andSGLb are formed as a gate metal pattern on a bottom substrate 60 inparallel with each other. Data and readout lines DL and ROL crossingwith the gate metal pattern are formed as a data metal pattern on a gateinsulating layer 62 in parallel with each other.

A pixel TFT Tpx includes a gate electrode 22 a protruding from the gateline GLi, a semiconductor layer 24 a overlapped with the gate electrode22 a by leaving the gate insulating layer 62 in-between, a sourceelectrode 26 a protruding from the data line DL to be overlapped withthe semiconductor layer 24 a, and a drain electrode 28 a connected to apixel electrode 32 via a contact hole 40 a of a passivation layer 64 byopposing the source electrode 26 a in the overlapping part with thesemiconductor layer 24 a. The semiconductor layer 24 a includes anactive layer forming a channel between the source electrode 26 a and thedrain electrode 28 a and an ohmic contact layer provided to theoverlapping part between the source and drain electrodes 26 a and 28 afor the ohmic contact between the source and drain electrodes 26 a and28 a.

A transparent common electrode 30 connected to the common line CLi isprovided to each pixel area defined by the crossing of the common lineCLi, the gate line GLi and the data line DL. The transparent commonelectrode 30 is formed on the substrate 60, on which the common line CLihas been formed, in a manner of being partially overlapped with thecommon line CLi before the gate insulating layer 62 is formed. Atransparent pixel electrode 34 is formed on the passivation layer to beoverlapped with the common electrode 30. The transparent pixel electrode34 includes a plurality of inclining slits 34 configured symmetric inlength direction to drive a liquid crystal layer by forming a horizontalelectric field together with the common electrode 30. And, a storagecapacitor Cs is generated as the pixel electrode 34 and the commonelectrode 30 are overlapped with each other.

In a space between the gate line GLi and a common line (not shown in thedrawings) of a next stage, a touch sensor including first and secondsensor gate lines SGLa and SGLb, a sensing electrode 20 and first andsecond sensor TFTs Tsw1 and Tsw2 is formed.

The first and second sensor gate lines SGLa and SGLb and the sensingelectrode 20 are formed of gate metal together with the gate line GLiand the common line CLi. And, a power line PL and a readout line ROL areformed of data meal together with the data line DL. The sensingelectrode 20 may be formed together with the common electrode 30 and thepixel electrode 34.

The first sensor TFT Tsw1 includes a gate electrode 22 d protruding fromthe first sensor gate line SGLa, a semiconductor layer 24 d overlappedwith the gate electrode 22 d by leaving the gate insulating layer 62in-between, a source electrode 26 d protruding from the power line PL tobe overlapped with the semiconductor layer 24 d, and a drain electrode28 d connected to the sensing electrode 20 by opposing the sourceelectrode 26 d at an overlapping part with the semiconductor layer 24 d.The drain electrode 28 d is connected to one end portion of the sensingelectrode 20 via a contact hole 40 f overlapped with one end portion ofthe sensing electrode 20 by perforating the passivation layer 64 and thegate insulating layer 62 both and a contact electrode 38 d formed on thepassivation layer 64 by penetrating the contact hole 40 f. The firstsensor TFT may be connected to the common line CL instead of the powerline PL. In this case, the power line PL may be omitted.

The second sensor TFT TSM2 includes a gate electrode 22 b protrudingfrom the second sensor ate line SGLb, a semiconductor layer 24 boverlapped with the gate electrode 22 b by leaving the gate insulatinglayer 62 in-between, a source electrode 26 b protruding from the readoutline ROL to be overlapped with the semiconductor layer 24 b, and a drainelectrode 28 b connected to the sensing electrode 20 by opposing thesource electrode 26 b at an overlapping part with the semiconductorlayer 24 b. The drain electrode 28 b is connected to the other endportion of the sensing electrode 20 via a contact hole 40 g overlappedwith the other end portion of the sensing electrode 20 by perforatingthe passivation layer 64 and the gate insulating layer 62 both and acontact electrode 38 e formed on the passivation layer 64 by penetratingthe contact hole 40 g.

A method of fabricating the TFT substrate shown in FIG. 6 and FIG. 7 isdescribed as follows.

First of all, a gate metal pattern is formed on a substrate. Inparticular, the gate metal pattern includes a gate line GLi, a commonline CLi, a sensing electrode 20, first and second sensing gate linesSGLa and SGLb, a gate electrode 22 a of a pixel TFT Tpx, and gateelectrodes 22 d and 22 b of first and second sensor TFTs Tsw1 and Tsw2.

A transparent electrode 30 connected to the common line CLi is formed ineach pixel area.

A gate insulating layer 62 is formed on the substrate 60 including thecommon electrode 30. A semiconductor pattern including a semiconductorlayer 24 a of the pixel TFT Tpx, a semiconductor layer 24 d of the firstsensor TFT Tsw1, and a semiconductor layer 24 b of the second sensor TFTTsw2 is then formed on the gate insulating layer 62.

A data metal pattern is formed on the gate insulating layer 62 on whichthe semiconductor pattern has been formed. In this case, the data metalpattern includes a data line DL, a readout line ROL, a power line PL,source and drain electrodes 26 a and 28 a of the pixel TFT Tpx, sourceand drain electrodes 26 d and 28 d of the first sensor TFT Tsw1, andsource and drain electrodes 26 b and 28 b of the second sensor TFT Tsw2.

A passivation layer 64 is formed on the gate insulating layer 62 onwhich the data metal pattern has been formed. And, a contact hole 40 aperforating the passivation layer 64 and contact holes 40 f and 40 grespectively perforating the passivation layer 64 and the gateinsulating layer 62 are then formed.

Subsequently, a transparent conductive pattern including a pixelelectrode 32 and contact electrodes 38 d and 38 e is formed on thepassivation layer 64.

Thus, an LCD device according to the present invention can have anembedded touch sensor using a TFT substrate fabricating process as itis.

Meanwhile, in FIG. 6 and FIG. 7, a horizontal electric field is formedusing the transparent common electrode 30 and the transparent pixelelectrode 32 having a plurality of the inclining slits 34 to beinsulatedly overlapped with the common electrode 30 for example.Alternatively, another pixel structure can be formed in a manner that acommon electrode and a pixel electrode are formed in a finger shape toform a horizontal electric field by finger parts of the common and pixelelectrodes alternating with each other. In this case, the common orpixel electrode in the finger shape can be formed of non-transparentmetal.

As mentioned in the foregoing description, the present inventionprovides the following effects and/or advantages.

First of all, the present invention is configured to have a touch sensorembedded in a TFT (thin film transistor) substrate, thereby enabling itsslimness and lightness and reducing a manufacturing cost.

Secondly, the present invention includes a touch sensor of a matrixtype, thereby detecting a multi-touch.

Thirdly, the present invention provides a simplified touch sensor fordetecting a touch via electrostatic capacitance to each space betweenneighboring pixel groups, each of which includes a plurality of pixels,thereby raising an opening ratio.

Fourthly, the present invention fabricates a touch sensor by a TFTsubstrate fabricating process as it is, thereby simplifying a wholeprocess to reduce a manufacturing cost.

Fifthly, the present invention drives a liquid crystal display device bydiscriminating a data writing interval and a touch sensing interval fromeach other, thereby preventing image quality degradation due tointerference of a touch sensor.

Finally, since a sensing signal outputted to a readout line via a secondsensor TFT from a sensing electrode having detected a touch depends on asum (Cf+Cpara) of electrostatic capacitance of a sensing capacitor and aparasitic electrostatic capacitance (Cpara) and a voltage difference(Vd−Vref) between a power source voltage supplied to the sensingelectrode and a reference voltage supplied to the readout line, wherebya precise sensing signal can be outputted irrespective of a thresholdvoltage (Vth) of the second sensor TFT.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of fabricating a touch sensor embedded liquid crystaldisplay device, comprising the steps of: forming a gate metal patternincluding gate electrodes of a pixel thin film transistor and first andsecond sensor thin film transistors on a substrate together with a gateline, a common line and first and second sensor gate lines; forming acommon electrode connected to the common line; forming a gate insulatinglayer on the substrate having the gate metal pattern and the commonelectrode formed thereon; forming semiconductor layers of the pixel andfirst and second sensor thin film transistors on the gate insulatinglayer, respectively; forming a data metal pattern including source anddrain electrodes of the pixel and first and second sensor thin filmtransistors on the gate insulating layer having the semiconductor layersformed thereon together with a data line, a power line and a readoutline; forming a passivation layer to cover the data metal pattern;forming a plurality of contact holes in the passivation layer; forming apixel electrode on the passivation layer to be connected to the drainelectrode of the pixel thin film transistor via the contact hole to forma horizontal electric field with the common electrode; and forming asensing electrode together with the gate line, the common electrode, orthe pixel electrode.
 2. The method of claim 1, wherein the gate, sourceand drain electrodes of the first sensor thin film transistor areconnected to the first sensor gate line, the power line and one endportion of the sensing electrode, respectively and wherein the gate,source and drain electrodes of the second sensor thin film transistorare connected to the second sensor gate line, the readout line and theother end portion of the sensing electrode, respectively.
 3. The methodof claim 1, wherein the sensing electrode is independently formed foreach touch sensor, wherein the readout line and the power line areformed in parallel with the data line by leaving a plurality of datalines in-between to be connected to a plurality of touch sensorsarranged in length direction, and wherein the first and second sensorgate lines are formed in parallel with the gate line to be connected toa plurality of touch sensors arranged in width direction.